A pulsed power amplifier which may be used in GSM mobile radio transmitters is described in UK patent application no. 8826918.8, the disclosure of which is incorporated herein by reference. This application discloses a burst modulated power amplifier whose output power characteristics upon turn-on and turn-off are controlled by power control signals which are dependent on a sequence of values stored in a memory of a power control section of the power amplifier. The power amplifier can operate at a number of different output power levels and a sequence of values is stored in the memory for each of these power levels. Once a power level has been selected, the corresponding sequence of values is selected and read from the memory.
The output power of a GSM mobile radio transmitter must be adjustable between sixteen power levels. In order to account for tolerance factors within the amplifier which will affect the ultimate output power, there are generally sixteen nominal power levels which are each split into four sub-levels close to the nominal value. A transmit controller of the power control section can then determine which of the sixty-four sublevels is best to represent each one of the sixteen nominal power levels. There are therefore sixty-four sequences of values stored in the memory corresponding to the sixty-four power levels.
Each of the sequences of values represents a ramp-up waveform and a ramp-down waveform corresponding to turn-on and turn-off respectively. One ramp-up waveform can be satisfactorily represented by a sequence of 64 bytes (512 bits) to be stored in the memory and one ramp-down waveform can be satisfactorily represented by a sequence of 64 bytes to be stored in the memory. Thus, the total number of bytes of memory required to store the sixty-four sequences of values is 8192 bytes (65536 bits). This is significantly large particularly when the power control section is integrated in an integrated circuit.
It is therefore desirable to reduce the number of bytes of memory required to store all the sequences of values for the different power levels.